The invention relates to a spring-loaded brake with a first housing section connected to a first brake shoe and a second housing section connected to a second brake shoe and with an actuation device, by means of which the first and the second housing section are capable of movement relative to one another. Such spring-loaded brakes are used, for example, for the securing of drive trains, in order to prevent the risk that, in the event of an operational fault, the machines connected to the drive trains run uncontrolled and wild. Thus, for example, spring-loaded brakes are used in particular on conveyor belts or chain conveyors, with which bulky material mined underground, such as coal, rock, or ore, is conveyed over long transport distances. With these devices, spring-loaded brakes prevent the risk that, in the event of a failure in the drive system, the belt with the material lying on it runs back uncontrolled along the conveying stretch or starts running under its own dynamic forces.
For this purpose, known spring-loaded brakes are equipped with an actuation device, designed as a rule as a spring package, by means of which the brake shoes, mounted on bearings in a jointed manner, equipped in each case with a brake lining, will automatically be moved into the braking position in the event of the removal of a counter-force applied via the brake caliper arm.
The advantage of the known spring-loaded brakes consists of the xe2x80x9cfail-safe behaviourxe2x80x9d explained heretofore, by means of which it can be ensured that a braking effect will always be reliably applied even if no further external energy sources are available for creating the braking force. Problems arise, however, in that the brake linings of the brake shoes are subject to wear. This wear depends on the frequency of the braking procedures, the braking time, and the scale of the braking force taking effect in each case. With increasing wear of the brake linings, the path increases over which the housing parts must be moved against one another, in order to reach the braking position. The consequence of this is that, if a spring package is used, the braking force of the braking device likewise decreases as the wear increases. For this reason it is necessary for the wear on the brake linings to be monitored and for the tension of the spring package to be adjusted. If an excessive degree of wear is detected, the connection between the housing parts and the spring package is adjusted in such a way that the braking force lies at the maximum permissible limit value.
In order to avoid manual adjustment, the principle is known of providing for a fluid-filled pressure buffer between the actuation device and at least one of the housing parts. This pressure buffer is connected to a pressure storage vessel, in which fluid is stored under pressure. In such a system, in the event of the braking force dropping because of wear, the fluid buffer is filled up with fluid under pressure to such a degree that the reduction in braking force caused by the wear is compensated for. In this way, the decrease in braking force otherwise inherent with brake wear will be automatically compensated for, and it will be ensured that the same braking force will still be uniformly available in the event of a fault.
In order to avoid overheating of the brake disks due to the brake linings chafing them or coming in contact with them during the operation of the drive, and therefore to a large extent avoiding the risk of fire, it is necessary for the air passage of the brake linings to be monitored, so that the risk can be avoided of the machine being started with inadequately vented brakes. For this purpose, the known spring-loaded brakes are equipped with an eccentric disk, which is connected to one of the housing parts. A limit switch is provided on the other housing part, by means of which, for example, the energy supply of a motor is controlled. The eccentric disk in this situation is adjusted in such a way that the limit switch is closed and the motor supplied with energy when the spring-loaded brake is vented, i.e. is out of action. If the limit switch is not reached, the motor must be prevented from starting.
This combination of limit switch and eccentric disk does indeed allow for the control of a motor with simple and robust means. It is however impossible in this manner to monitor the wear of the spring-loaded brake reliably in such a way that, on the one hand, a signal is always received relating to the need for the brake linings to be replaced, and, on the other hand, the brake linings can also be used for an optimum period of time. In addition to this, the mechanical elements of the limit switch/eccentric disk combination have proved in practice to be prone to failure, since on the one hand they must be freely accessible for adjustment and readjustment purposes, and, on the other, they are always subject to the risk of damage due to falling material. In addition to this, the wilfully or unintentionally incorrect setting of the eccentric disk may lead to faulty function of the limit switch.
In addition to the prior art known from practice, as described heretofore, a brake caliper unit is known from DE 195 14 463 C1, of the generic type of the invention, for the disk brakes of vehicles, and railed vehicles in particular, in which one brake caliper arm is connected directly to the housing and the other brake caliper arm is connected by means of a gear system. With this known brake caliper unit, too, the problem arises of identifying wear of the brake lining in good time, and of avoiding malfunction of the brake in the event of inadequate venting.
The objective of the invention is of creating a spring-loaded brake of the type referred to in the preamble, in which the air passage and the wear can be monitored reliably and in a simple manner.
This objective is achieved according to the invention in that a spring-loaded brake of this type is equipped with a measuring device, which continually monitors the change in the relative position of the housing parts.
With a spring-loaded brake designed according to the invention, continuous monitoring of the relative position of the housing parts can be effected. In this way, information is always available from which can be derived, on the one hand, the air passage which is covered in each venting procedure, and, on the other, the current state of wear of the brake linings in each case. This makes it possible, with low technical effort, to make an assessment at any time of the air passage, the state of wear, and, inherently associated with this, of the functionality of the spring-loaded brake. It is accordingly possible to display, with a high degree of reliability, the position of the brake shoes in the vented state. With equally high precision, the moment of time can also be determined at which the replacement of the brake linings is in fact required.
By means of the continuous acquisition of the relative position of the housing parts, made possible by the invention, assessments can be made of the effective size of the air passage covered during each venting procedure. These signals form the basis for the generation of control signals for the operation of the drive system connected to the brake equipped according to the invention. If it is ascertained, for example, that the air passage is too small, the drive is not allowed to start up. On the other hand, the risk pertains that overheating of the brake may occur due to chafing brake shoes. If it is ascertained, by contrast, that the air passage is too large, this means that a readjustment of the air passage limits must be carried out.
In the braked position, too, the measuring device provided for according to the invention supplies a signal which is important for the assessment of the operational state.
For example, it is possible to conclude from the position of the brake caliper arms, determined by means of the measuring device in the braked position, whether the brake shoes of the brake are showing sufficient strength.
It is no longer necessary to make an adjustment of the measuring device after each replacement of the brake shoes, since the xe2x80x9czero statexe2x80x9d in which the housing parts are located relative to one another after brake shoe replacement can be automatically determined. In this way it is assured that no error function arises during monitoring due to faulty basic settings.
Because of the possibility of continuous determination of the positional changes of the housing parts, it is also no longer required to make regular checks of the functional performance of the measuring device by way of a visual inspection, or to carry out adjustments on mechanical components. Instead of this, the measuring device can be arranged with no problem at a protected location in such a way that mechanical damage by external forces can be avoided.
This applies in particular in situations in which the measuring device comprises a measuring rod, featuring contacts which are actuated by the effects of a magnetic field, this rod being coupled to the first of the housing parts and being capable of movement by a magnetic field, this magnetic field being created by a device connected to the second housing part, whereby the device creating the magnetic field and the measuring rod are capable of movement relative to one another. The rod and the device creating the magnetic field serve in this situation to determine changes in position, and are robust components, not prone to faults and free of maintenance, which, if space is limited, can be arranged in a secure and protected manner in housing sections of the housing parts.
With such embodiments of the spring-loaded brake according to the invention, in which provision is made for a manually-adjustable or automatic device for wear compensation, the actual wear of the brake can be determined from the information derived from the continuous monitoring of the relative position of the housing parts. Accordingly, it is possible to determine the beginning and end of the air passage which is covered for releasing the brake, every time the device which is braked by the brake is taken into operation. It is true that the braking force does not change because of the wear compensation, but the wear always results in a change in the position of the start point of the air passage. These points can be determined and evaluated with no problem with spring-loaded brakes designed according to the invention, with the result that, even with wear-compensated brakes, an effective and continuous check is possible on the state of the spring-loaded brake.
An embodiment of a spring-loaded brake according to the invention, suitable for practical application, and operating with a high level of operational reliability, is characterised in that the actuation device exercises an elastic force, which automatically moves the housing parts into a relative position, in which the brake caliper arms with the brake shoes are in their braking position.
In this situation, a further development of this embodiment, likewise to the purpose, is characterised in that a venting device is provided for, which, when force is applied, brings the housing parts into a relative position, against the force of the actuating device, in which the brake caliper arms with the brake shoes are without effect. This venting device operates for preference hydraulically or pneumatically, since with such a mode of operation, substantial forces can be generated in an operationally safe manner, especially underground, without the risk inherent with the use of high electrical energy values.
In the event of a hydraulically or pneumatically-actuatable venting device being present, the device can be controlled by means of a valve combination, which features a inflow passage for the inflow of pressure fluid when force is applied, and an outflow passage for the outflow of pressure fluid. It is to advantage in this connection if a choke is arranged in the outflow passage of the valve combination, the choke effect of which is capable of being altered. By a suitable adjustment of the choke, the time can be changed at which the pressure fluid escapes from the venting device at depressurisation. In this way, a desired closing time for the spring-loaded brake can be set. Accordingly, for example, a high choking effect of the escaping pressure fluid has the effect of prolonging the closure time, while a slight choking effect of the escaping air results in a rapid closure of the brakes. The valves and all other operational states of a spring-loaded brake according to the invention can of course be controlled manually. In order to achieve automatic control, however, a control device should for preference be provided for which controls the valve combination as a function of control signals.
An especially compact design form of a spring-loaded brake according to the invention is derived if the valve combination is carried by one of the housing parts.
A further embodiment of the invention, which substantially improves the availability and operational reliability of a spring-loaded brake according to the invention, is characterised in that an evaluation device is provided which evaluates the measurement signal delivered by the measuring device. This evaluation device can be used for ongoing monitoring of the functional performance of the spring-loaded brake. In particular, it is possible with the evaluation device to determine automatically the state of wear of the brake. In this situation, the evaluation device makes use of the measured values which are constantly provided by the measuring device. The measured signals provide information about the wear state of the brake linings, when the evaluation device determines the path covered between a start and end position of the housing parts during a braking or venting procedure of the spring-loaded brake. The longer this path, the further the wear of the linings has progressed.
It is just as much to the purpose if the evaluation device, as am alternative or as a supplement, determines the time which the housing parts require, during a braking or venting procedure, to reach their start or end position. The length of the time interval which elapses from the start of the spring-loaded brake moving apart or closing respectively provides a direct indication of the state of the brake as a whole. Accordingly, it must be assumed that there is a defect in the venting device if the venting device requires more time for venting than a maximum permitted duration. Likewise, it can be assumed that there is a defect in the actuation device if the automatic closure of the brake does not take place within a specific time. As a result, it is favourable if the evaluation device compares the result of each individual evaluation with a reference value allocated to this result, and issues a signal as a function of the outcome of the comparison. In consideration of the often rough and changeable external influences, and the conditions they induce, under which spring-loaded brakes according to the invention are used, it is to the purpose in this connection if the evaluation device does not issue a signal indicating a fault until the result of the evaluation deviates from the reference value allocated to this result, and taking a tolerance range into account.
A simple examination of the operational and wear state of a spring-loaded brake according to the invention can be achieved if the evaluation device is coupled to a display device, which issues a visual or audible signal as a function of the signal issued by the evaluation device. It is of course equally possible for the signals of the evaluation device to be transferred to a central monitoring and control point.
Inasmuch as the evaluation device is carried by one of the housing parts, a compact structural unit is provided, which need only be connected to a few non-sensitive supply leads and, if applicable, signal transfer leads. This applies in particular if the valve combination for controlling the venting device is also arranged on a housing part.
The closing behaviour of a spring-loaded brake according to the invention can be determined in a simple fashion in that, in the presence of a control device, a valve combination, and an evaluation device, the control device controls the valve combination as a function of signals from the evaluation device. It is to advantage, in this connection, if the venting device is capable of being brought into a second operational state by means of an actuator which is capable of being activated independently of the control device. Such an actuator can, for example, activate a slide valve, in one position of which pressure fluid escapes from the venting device, while in its other setting pressure fluid flows into the venting device. The manually actuatable device makes it possible, during maintenance work, for the brake to be opened and closed independently of the signals from the control device.
In addition to this, it is possible for the closure and/or air behaviour of a brake according to the invention to be adjusted by the actuator, operating independently of the control device. This is made possible, according to the invention, by the evaluation device storing as a reference value the time determined, in the event of manually-induced opening, for the depressurisation of the venting device which then takes place. This reference value is then retained for all subsequent closure procedures until a new reference value is presented. With this embodiment of the invention, the unit formed from the measuring device, the evaluation device, and the control device, operates in the manner of a learning system, which can be adapted with the greatest possible flexibility to the most widely differing braking tasks. In this situation the simple adjustability of the closure time described has proved to be especially advantageous in situations in which conveyor belts of considerable length, such as are encountered underground, are intended to be braked by several spring-loaded brakes according to the invention, spaced at intervals from one another. If the braking is carried out in cascade fashion with temporal delay, the belts can be braked in a gradual and progressive manner with temporal displacement, in their direction of conveying. In this way, the risk can be avoided, which would otherwise pertain, of the belts buckling because of their individual kinetic energy in each case.
A further improvement in the operational reliability and behaviour of a spring-loaded brake according to the invention can be achieved in the event of a fault in that a pressure monitoring device is provided for, which monitors the pressure of the pressure fluid, which is contained in a supply line providing the venting device with pressure fluid. In the event of a loss of pressure, such a pressure monitoring device issues an alarm signal, which will, for example, prevent the attempt being made of venting the spring-loaded brake with an insufficient pressure of the pressure medium.
An embodiment of the invention which has proved to be particularly important in practice is characterised in that the evaluation device comprises a signal generator, the signal from which sets an initial state. The possibility of setting an initial state as a function of a corresponding signal is of significance, for example, if after maintenance work the state of the spring-loaded brake is to be readjusted, and, inherent in this, the reference points have changed for the values monitored by the measuring device. Inasmuch as the evaluation device is brought into a specific state by a signal, in which the current reference points in each case are set as starting point values for the measurements and evaluations carried out subsequently, it is in principle possible for every operational state of the spring-loaded brake to be defined as an initial state. This makes it possible on the one hand to achieve versatility of use and easy adaptation of the evaluation device to the most widely differing operational conditions; on the other hand, this will also ensure that the measurement and evaluation are always carried out under optimum peripheral conditions in respect of reproducibility.
It is also favourable in this connection if the evaluation device comprises a switch which is capable of actuation without being touched, and which, on actuation, generates the relevant signal for setting the initial state. Such a switch makes it possible, in a simple manner, to prevent impermissible outside intervention, in that it is installed with a cover in a housing of the evaluation device, and is actuated by an actuation force taking effect from outside, without touch. This can be achieved, for example, if the switch comprises a switching element which is magnetically sensitive.
If provision is made for the evaluation device to be capable of being set into an initial state by means of a signal, this should only be possible if the spring-loaded brake or the device braked by the spring-loaded brake is in a certain specific operational state. In this way it is possible to prevent the risk of a spring-loaded brake in a threadbared state being further operated by manipulations.